It doubles risk of developing psychotic disorders, including schizophrenia

Heavy use in adolescence appears to impair intellectual development

Driving after smoking cannabis doubles risk of having a car crash
Study's author said: 'If cannabis is not addictive then neither is heroin.'

[In 2014] the drug was legal in two states - Washington and Colorado
A further 21 states have allowed it to be used for medicinal purposes
Obama said earlier this year cannabis is not as dangerous as alcohol

A definitive 20-year study into the effects of long-term cannabis use has demolished the argument that the drug is safe.
Cannabis is highly addictive, causes mental health problems and opens the door to hard drugs, the study found.
The paper by Professor Wayne Hall, a drugs advisor to the World Health Organisation, builds a compelling case against those who deny the devastation cannabis wreaks on the brain.